one `JSON` file in the `PHP` server to collect the orders from different customers

Unlike an ASP or PHP page, a JSON file does not "collect" anything. Based on what you've provided, unless you are doing something totally wrong, there should be no way for it to become locked. If multiple clients request the same JSON file, the web server will deliver the file to each client without issue.

AndroidVH wrote:

Any suggestion?

The whole "upload a file containing a customer number and/or order" approach seems way wrong to me.

When you make contact with a web server, a one-on-one relationship has been established. When you interact with a web page (e.g., PHP file), you are doing so with your "copy" of it. If some other client is also interacting with that same page, again it's on their own "copy" of it. The web server keeps track of all those connections (up to some upper limit).

Admittedly, I may be completely wrong on this. It borders on ecommerce which I have zero experience with. But what you are doing just seems kludgy and prone to error.

I was trying to fetch JSON data into a RecyclerView using Retrofit 2. I also implemented pagination. Now for testing, I changed the JSON URL as if it will only show `5`items per page. The page number can be changed by adding "&page=`PAGE#`" at the end of the JSON URL (where PAGE# is integer value starting from 1 and if no Page no is mentioned, it will show by default the first page).

Problem: I have successfully added every page into the Recyclerview. But, it is adding the last page items twice, sometimes it is adding 3 times. Like this.
I am unable to find the problem. The step by step debugging does not help. Please help me. I am learning these so if you help me I would really appreciate it.

I'm writing a program using bound service with Inter Process Communication(IPC). The goal is to send the generated data in a thread (DataExchange) from the service to the mainActivity, using Messenger and Hanler. When the data is placed in the message queue from run method, I'm unable to receive it in the activityHandler (mainActivity). fortunatly I can receive the data in the serviceHandler (Local communication), however when I try to send the same message from the serviceHandler (service) to activityHandler (mainActivity), I'm getting a FATAL EXCETION
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.os.Messenger.send(android.os.Message)' on a null object reference
Someone please help

You need to go back to the original error and find out why msg or replyTo are null. As I said earlier, we cannot diagnose the state of your objects. If nothing obvious shows up then you need to check the documentation to make sure that you are creating the objects correctly. Randomly changing the code before you have diagnosed the error is not likely to help you.

Which is probably a good reason to start with a few simpler programs before diving into services and IPC programs. Tracking down null pointer exceptions is a fundamental task, so if that is giving you trouble, it's time to take a step (or two) back and get the basics nailed down real good.

Sir I have problem. Let suppose that I have data like 23,56,89,88,90,1234,3445. now I want to add them all and want to get result. but this code is giving me result like that 23+56+36=92 not 115. mean it make addition of just to previous values

You are treating each part of the calculation as the complete result, rather than saving the interim value. When you click the + button you set Value1 equal to the number in the txt box. But next time you press the + button you overwrite Value1. So typing 23+56+36 actually only gives the result of 56+36, which is 92. You need to keep a running total as each operator button is pressed. So the sequence should be something like:

Set Value1 to zero
set next operator to +
DO
if an operator button is pressed
if it is the '=' operator
display the result
else
parse the text into the number
apply the current operation to Value1 (i.e add, subtract etc. this number to Value1)
set the 'next' operator to the pressed button
WHILE operator is not '='

What EXACTLY are you needing help with? Do you have an Android app that is using a WebView control and you are wanting to know if a requested page could not be loaded, or do you need help displaying a "message box" to the user?

If the former, call setWebViewClient() on your WebView object and listen for the 404 error in the onReceivedError() method.

If you really want to do it:
Because source code files are text files, it is a job for simple search & replace which can be automated using regular expressions iterating over the values of an input file (CSV would be better / simpler to use than Excel) and a list of source files. With Linux I would use a shell script for all the stuff except the replace which can be done with sed.